1. Technical Field
The present disclosure relates to an image processing technology, and in particular, to a white balance process for digital color images.
2. Description of Related Art
Generally speaking, colors that reflect off an object depend on color of the light sources. A human brain is able to detect and make corrections for this type of color change. On a sunny day, a cloudy day, or in a room with light bulbs or fluorescent lamps, a human eye can adapt to the changes in color under different light sources and it will not affect the way in which humans perceive white objects. However, “white color” generated by different light sources is perceived differently by a digital image capturing device. For example, the actual colors in a photo tends to be yellowish if it is taken in a room illuminated with tungsten lamps (light bulbs), and it tends to be lightly bluish or reddish if it is taken in other environments. In order to make the colors in the photos consistent with the colors perceived by human eye, the digital image capturing device has to mimic the human brain and to adjust the colors according to the light source. It has to define the white color so that, as far as possible, it is the same in the photo as it is in the white color perceived by the human eyes. This type of adjustment is known as “white balance.”
In prior art, a color histogram stretching (CHS) method is used to adjust the white balance for the image, raw histograms of red (R), green (G), and blue (B) are created as three color channels which are re-quantized into a range of 0-255, and the adjusted result shows that this method has characteristics of immediacy with only small error. However, the color histogram stretching method needs a larger memory space, to estimate a reference black color and a reference white color in the light sources. Therefore, it is necessary to provide a white balance adjustment method which maintains a high image contrast.